The present invention relates to an improvement of an automatic document sheet conveyance device to be used for a recording apparatus such as an electrophotographic copying machine.
An automatic document sheet conveyance device is usually mounted, when it is used, on a document table glass (platen glass) in an image exposure section of a copying machine and others. In a copying machine having a movable optical system on which the automatic document sheet conveyance device is mounted, a document in a sheet form (hereinafter referred to simply as a document) fed out one sheet by one sheet from a document tray (document stacking portion) on which documents are stacked is conveyed by a conveyance belt onto a platen glass where the document is exposed to an exposure lamp, and then ejected onto a document ejection tray.
In a document change operation on a platen glass by means of such an automatic document sheet conveyance device, both conveyance and ejection need to be performed in a short period of time for the purpose of avoiding the reduction of productivity of copying. Namely, it is preferable that the copying speed CPM (number of copies made in a minute) in an image forming process in a main frame of a copying machine is mostly the same as the document handling speed OPM (number of documents handled in a minute) in the automatic document sheet conveyance device.
For that purpose, if document changing is made within a period of returning time of a scanning optical system on the occasion of document changing by means of an automatic document sheet conveyance device wherein a document is automatically fed to and ejected from a platen glass, it is possible to keep the productivity of copying at 100% and there is no waste time.
In a copying machine capable of copying at a high speed, a document conveyance speed covering from the position for document double feed prevention in document stacking portion to the document stopping position as well as a document ejection speed for ejecting out the document from the document stopping position are set to be high.
However, when a document ejecting speed is set to be high, a contact area between a running conveyance belt and a platen glass, within a predetermined period of time, increases during the course of document ejection wherein a document moves on the platen glass, and thereby friction resistance also increases. Due to the increase in the friction resistance of the conveyance belt, the load for a driving motor increases, resulting in an increase of power consumption and over heat caused by an excessive load on the driving motor. Further, the conveyance belt slips on a driving roller that drives the conveyance belt and the driving roller runs idle, resulting in damage of the conveyance belt, the driving roller and bearings. Therefore, a large-sized motor having a large driving torque is needed, which is a problem.
The first object of the invention is to solve the aforesaid problems in an automatic document sheet conveyance device and thereby to improve the productivity of copying.
In a conventional copying machine, even when continuous copying is suspended in a series of continuous copying because of exhaustion of copy paper, it is possible to start the continuous copying again for continuation by pushing a start button after loading copy papers without necessity of setting the number of necessary copies in the period of the suspension. Therefore, it is possible to obtain easily the copies in exact quantity set in the beginning for each of documents stacked on a document tray. However, when the setting of the number of copies such as a ten-key operation including the pressing of a clear key in the period of suspension caused by the exhausting of copy papers, copying operation started thereafter by pushing a start button becomes, without being a continuation of a series of copying operations suspended on the half way, a new series of copying operations for obtaining copies in quantity set newly. In that case, a conventional copying machine has been arranged so that a document positioned at the exposure section when the number of copies has been set may be ejected onto a document ejection tray.
In a conventional copying machine such as one stated above, document conveyance from the document tray to the exposure section has always been made separately for each document. Therefore, when each document is conveyed to the exposure section, it equally and fully takes the period of time calculated by dividing the conveyance path length from the document tray to the exposure section by the conveyance speed. Thus, it takes time to finish a series of copying operations, which is a problem.
The invention has been devised also to solve the aforesaid problems, and the second object of the invention is to offer a copying machine provided with an automatic document sheet conveyance device wherein a series of copying operations by means of an automatic document sheet conveyance is performed efficiently and thereby the productivity of copying is high and it is further possible to start without trouble a series of copying operations by pushing a start button with new setting of the number of copies when the setting of the number of copies is made during the suspension caused by the exhausting of copy papers on the half way.
Further, in a conventional copying machine provided with an automatic document sheet conveyance device such as one stated above, the speed for ejecting a document in case of jamming taking place in a copy paper conveyance system has been the same as that for feeding the document into the exposure section and for ejecting, concurrently with the foregoing, the exposed document from the exposure section. For the purpose of raising the productivity of copying in a copying machine provided with an automatic document sheet conveyance device, therefore, when the speed for feeding the document to the exposure section is raised, and when a certain arrangement is made wherein the second document or thereafter is fed, while the preceding document is in the exposure section, to the standby position where the leading edge of the second document or thereafter is close to the trailing edge of the preceding document in the exposure section, and thus the second document or thereafter is fed to the exposure section concurrently with the ejection of the previous document, the document in the exposure section and the document in the standby position hit or overlap partially each other, resulting in jumping out of a document ejection tray or overlapping on the document ejection tray, causing the documents to be easily in wrong order.
The invention has been devised to solve also the aforesaid problems, and the third object of the invention is to offer a copying machine provided with an automatic document sheet conveyance device capable of making copies efficiently and capable of continuing copying operation easily despite jamming taking place in the copy paper transport path and further a document can always be ejected properly onto a document ejection tray.